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American Beaver

A beaver’s lips close behind its front teeth, allowing it to chomp trees with its mouth closed.

Glenn Chambers

Family:

Castoridae (beavers) in the order Rodentia

Description:

The American beaver is a large rodent associated with waterways and wetlands. It has webbed hind feet; a large, relatively hairless, horizontally flattened tail; a blunt head with small eyes and ears; a short neck; and a stout body. The color is a uniform dark brown above with lighter underparts and a blackish tail.

Similar species: Two other aquatic rodents in Missouri might be confused with beavers. The common muskrat, found statewide, has a long tail that is slightly flattened vertically, and it is a smaller animal, usually only weighing 2–4 pounds. The introduced nutria, which sometimes occurs in southeastern Missouri, has a tail that is round in cross-section, and at 15–25 pounds, it is intermediate in size between beaver and muskrat.

In Missouri, beavers live in and along streams, rivers, marshes, and small lakes. Though they are famous for dam building, in Missouri they are less likely to construct dams than they are in regions farther west and north. Instead, in our faster and fluctuating streams, they usually excavate a den in a high bank. In both lodges and bankside dens, the entrance is usually below water. Beaver restoration efforts have brought their numbers to levels allowing an annual harvest.

Foods:

In spring and fall, beavers eat woody and nonwoody vegetation. In summer, they eat mostly nonwoody plants; in winter, they eat mostly woody plants. Woody foods include the bark, new twigs, and new bark growth of a variety of trees and woody vines ranging from willows and cottonwood to oaks, hickories, sycamores, and wild grapevines. Nonwoody foods include corn, pond lilies, watercress, and many other herbaceous plants.

Distribution in Missouri:

Beavers occur statewide near streams and wetlands. They are least common in the Mississippi Lowlands.

Status:

Despite an extreme reduction in their colonies by about 1900, Missouri’s beaver population has been reestablished statewide.

Life cycle:

Beavers are usually nocturnal but may also come out in the daytime, especially in fall when they are busy gathering food and preparing their dams and lodges for winter. They live in colonies — family groups comprising an adult male and female and their yearlings and kits. Breeding begins in January and February, and a single litter of usually 3 or 4 young is born in April, May, or June. The young are weaned after about 6 weeks but remain with the family for about 2 years.

Beavers are harvested for their fur, which is used in coats and trimmings. Some people enjoy eating beaver meat. In the past, beaver fur, meat, and oil were immensely important in attracting both Native Americans and European settlers to our region.

Ecosystem connections:

Across the continent, the historic value of beaver damming is hard to estimate, when you consider their long-term impact on stream flow, creation of ponds, and causing silt to settle and create fertile valleys. This development of new habitats has a profound effect on the many other plants and animals requiring such conditions.

Signs & Tracks:

Front track:

3½ inches long

5 toes, though often only 3 or 4 toes leave a track.

Hind track:

6–7 inches long, 5 inches wide

5 toes, though often only 3 or 4 toes leave a track

toes are webbed, though the marks are not always distinct

hind track is often confused with goose tracks.

Other notes:

Beaver are common on banks of rivers and other aquatic habitats where trees are nearby.

On steep banks, look for scratch marks.

Hind tracks are positioned just in front of the front tracks, but often they land directly on top of the front tracks so that the front tracks are indistinguishable.

The flat tail often drags down the middle, sometimes obliterating foot tracks.

About Mammals in Missouri

More than 70 species of wild mammals live in Missouri: opossums; shrews and moles; bats; rabbits; woodchuck, squirrels, beaver, mice, voles, and other rodents; coyote, foxes, bear, raccoon, weasels, otter, mink, skunks, bobcat, and other carnivores; deer and elk; and more. Most of us recognize mammals easily — they have fur, are warm-blooded, nurse their young, and breathe air.